1. Field of the Invention
The present invention relates to a monitor system, and more particularly, to a focus compensation apparatus and method for performing focus compensation at the edge of the screen of a monitor system.
2. Description of the Related Art
A video signal is clamped to a black level voltage which is a constant direct current (DC) voltage representing the brightness of a picture, and the clamped video signal is scanned to the screen of a monitor through an electron gun. A contrast adjustor is provided in the monitor so that a user can adjust the contrast of a picture. When the contrast of a picture is adjusted by the user, focus compensation in accordance with the contrast adjustment may be needed.
As the size of the screen of a monitor becomes larger, the surface of the screen tends to become more aspheric, that is, flat. FIG. 1 is a schematic diagram showing a picture tube of a monitor as an example.
Referring to FIG. 1, an electron gun 110 receives a video signal VOUT, generates an electron beam, and controls the intensity of the electron beam to reproduce a picture on a screen 130. As shown in FIG. 1, when the screen 130 has an aspheric surface, the distances from the electron gun 110 to different portions of the screen 130 may be different. For example, the distance I1 or I3 between the electron gun 110 and the edges M of the screen 130 may be longer than the distance I2 between the electron gun 110 and the center N of the screen 130. In this case, a picture may be out of focus and more blurred at the edge of the screen 130 than at the center of the screen 130. A phenomenon in which a picture is out of focus at the edge of a screen can be eliminated by transforming a video signal into a parabolic format.
FIG. 2A is a diagram showing a video signal after the video signal, which corresponds to a single scanning line, is transformed into a parabolic format. FIG. 2B is a diagram showing the video signal corresponding to a single scanning line before it is transformed into a parabolic format.
Referring to FIGS. 1 through 2B, in a case in which the level of a video signal at the center N is equal to the level of the signal at the edge M as shown in FIG. 2B, the video signal is scanned to the center N and the edge M of the screen 130 at the same level. Since the edge M is farther from the electron gun 110 than the center N of the screen 130, the level of the scanned video signal appears lower at the edge M of the screen 130 than at the center N of the screen 130. Accordingly, even though a picture is in focus at the center N of the screen 130, the picture is gradually blurred from the center N toward the edge M.
In a case in which a video signal has a parabolic format in which the level of the video signal gradually increases from the center N toward the edge M as shown in FIG. 2A, the level of the video signal scanned to the edge M, which is farther than the center N from the electron gun 110, is higher than the level of the video signal scanned to the center N. In other words, a drop in the level of the video signal scanned to the edge M of the screen 130 due to the difference between the distances from the electron gun 110 to the edge M and to the center N of the screen 130, is compensated for. Accordingly, a picture can be in focus at the edge M of the screen 130 as well as at the center N of the screen 130.
When transforming a video signal into a parabolic format as shown in FIG. 2A, it is important to set a parabolic signal level P to an appropriate value. In other words, a ratio of the parabolic signal level P and a video signal level Q must be appropriately set to make a picture in focus at the edge M of the screen 130. For example, assuming that the focus of a picture is effectively adjusted at the edge of a screen when the parabolic signal level P is 10% of the video signal level Q, the ratio of the parabolic signal level P to the video signal level Q must not be changed even when the video signal level Q is changed by a user externally operating the monitor system. In other words, when a user changes the contrast so that the video signal level Q is changed, the parabolic signal level P must also be changed to maintain the ratio of the parabolic signal level P to the video signal level Q at 10%.
Conventionally, a parabolic signal is generated by an externally provided separate chip. When a parabolic signal is generated by an external chip, adjustment of contrast by a user and generation of a parabolic signal according to the contrast adjustment are separately performed. That is, in such a system, when a user varies contrast, the parabolic signal level P is not automatically varied. Accordingly, additional operation is needed for varying the parabolic signal level P in response to the variation of the video signal level Q so as to maintain a predetermined ratio of the parabolic signal level P to the video signal level Q. As described above, since contrast adjustment and focus compensation are separately performed when a parabolic signal is generated by an external chip, an operation for adjusting the focus at the edge of a screen is difficult, and a circuit used to perform the adjustment may be complex and, therefore, expensive.
To solve the above problems, it is a first objective of the present invention to provide a focus compensation apparatus for efficient focus compensation at the edge of the screen of a monitor.
It is a second objective of the present invention to provide a focus compensation method for efficient focus compensation at the edge of the screen of a monitor.
It is a third objective of the present invention to provide a parabolic signal generator used in the focus compensation apparatus, for generating a parabolic signal, the waveform of which can be varied.
Accordingly, in one aspect, the invention is directed to a focus compensation apparatus for adjusting a focus at the edge of a monitor screen in a monitor system. The focus compensation apparatus includes a parabolic signal generation circuit for generating a parabolic signal in synchronization with a horizontal flyback pulse, the waveform of the parabolic signal varying in response to first and second control signals. The focus compensation apparatus also includes a video signal focus compensator for adjusting the gain of an input video signal such that the gain increases from the center of the monitor screen toward the edge of the monitor screen in response to the parabolic signal, and for outputting a gain adjusted video signal as a focus-compensated video signal.
In one embodiment, the first control signal is an auxiliary contrast control signal for achieving white balance by adjusting the contrast of red, green and blue signals which constitute the input video signal. The video signal focus compensator can adjust the contrast of the focus-compensated video signal in response to a contrast control signal.
In another embodiment, the first control signal is a contrast control signal for adjusting the contrast of the input video signal. The video signal focus compensator can adjust the contrast of red, green and blue signals constituting the focus-compensated video signal in response to an auxiliary contrast control signal.
The parabolic signal generation circuit can include a first level adjustor, a horizontal parabolic signal generator, and a parabolic signal synthesizer. The first level adjustor generates a first signal having a level corresponding to the first control signal. The horizontal parabolic signal generator generates a horizontal parabolic signal in synchronization with the horizontal flyback pulse, wherein the waveform of the horizontal parabolic signal varies in response to the first signal and the second control signal. The parabolic signal synthesizer synthesizes the first signal and the horizontal parabolic signal and generates a synthesized result as the parabolic signal for controlling the input video signal, such that the gain of the input video signal increases from the center toward the edge of the monitor screen. In one embodiment, the horizontal parabolic signal generator includes (i) a first sawtooth generator for receiving the horizontal flyback pulse and generating a first sawtooth signal synchronized with the horizontal flyback pulse, (ii) a first multiplier for receiving the first sawtooth signal and squaring a linear section of the first sawtooth signal to generate a squared signal as a first square signal, (iii) a second level adjustor for receiving the first signal, adjusting the level of the first signal in response to the second control signal, and generating a level-adjusted first signal as a second signal, and (iv) a first parabolic amplitude adjustor for receiving the first square signal, controlling the amplitude of the first square signal to be the level of the second signal, and generating an amplitude-controlled signal as the horizontal parabolic signal.
In one embodiment, the parabolic signal generation circuit can also include a vertical parabolic signal generator for generating a vertical parabolic signal in synchronization with a vertical flyback pulse, the waveform of the vertical parabolic signal varying in response to the first signal and a third control signal. The parabolic signal synthesizer synthesizes the first signal, the horizontal parabolic signal and the vertical parabolic signal and generates a synthesized result as the parabolic signal. The vertical parabolic signal generator can include (i) a second sawtooth generator for receiving the vertical flyback pulse and generating a second sawtooth signal synchronized with the vertical flyback pulse, (ii) a second multiplier for receiving the second sawtooth signal and squaring a linear section of the second sawtooth signal to generate a squared signal as a second square signal, (iii) a third level adjustor for receiving the first signal, adjusting the level of the first signal in response to the third control signal, and generating a level-adjusted first signal as a third signal, and (iv) a second parabolic amplitude adjustor for receiving the second square signal, controlling the amplitude of the second square signal to be the level of the third signal, and generating an amplitude-controlled signal as the horizontal parabolic signal.
In another aspect, the invention is directed to a focus compensation method for adjusting focus at the edge of a monitor screen in a monitor system. The focus compensation method includes the steps of (a) generating a first signal having a level corresponding to a first control signal, (b) generating a horizontal parabolic signal in synchronization with a horizontal flyback pulse, the waveform of the horizontal parabolic signal varying in response to the first signal and a second control signal, (c) synthesizing the first signal and the horizontal parabolic signal to generate a parabolic signal, the level of the parabolic signal increasing from the center of the monitor screen toward the edge of the monitor screen, and (d) performing focus compensation such that the gain of the input video signal increases from the center of the monitor screen toward the edge of the monitor screen by adjusting the gain of the input video signal according to the parabolic signal.
In one embodiment, the first control signal is an auxiliary contrast control signal for achieving white balance by adjusting the contrast of red, green and blue signals constituting the input video signal. In another embodiment, the first control signal is a contrast control signal for adjusting the contrast of the input video signal.
In one embodiment, the step of generating a horizontal parabolic signal in synchronization with a horizontal flyback pulse includes (i) generating a first sawtooth signal synchronized with the horizontal flyback pulse, (ii) generating a first square signal by squaring a linear section of the first sawtooth signal, (iii) adjusting the level of the first signal according to the second control signal and generating a level-adjusted first signal as a second signal, and (iv) controlling the amplitude of the first square signal to be the level of the second signal and generating an amplitude-controlled signal as the horizontal parabolic signal.
In one embodiment, the method of the invention further includes generating a vertical parabolic signal in synchronization with a vertical flyback pulse after generating a horizontal parabolic signal in synchronization with a horizontal flyback pulse, wherein the waveform of the vertical parabolic signal varies in response to the first signal and a third control signal. Also, the step of synthesizing the first signal and the horizontal parabolic signal to generate a parabolic signal can include (i) synthesizing the first signal, the horizontal parabolic signal and the vertical parabolic signal and (ii) generating a synthesized result as the parabolic signal. The step of generating a vertical parabolic signal in synchronization with a vertical flyback pulse after generating a horizontal parabolic signal in synchronization with a horizontal flyback pulse can include (i) generating a second sawtooth signal synchronized with the vertical flyback pulse, (ii) generating a second square signal by squaring a linear section of the second sawtooth signal, (iii) adjusting the level of the first signal according to the third control signal and generating a level-adjusted first signal as a third signal, and (iv) controlling the amplitude of the second square signal to be the level of the third signal and generating an amplitude-controlled signal as the vertical parabolic signal.
In another aspect, the invention is directed to a parabolic signal generator used in a focus compensation apparatus. The parabolic signal generator includes a sawtooth generator, a multiplier, a level adjustor, a parabolic amplitude adjustor and a parabolic signal synthesizer. The sawtooth generator is for receiving a pulse signal and generating a sawtooth signal synchronized with the pulse signal. The multiplier receives the sawtooth signal and squares a linear section of the sawtooth signal to generate a square signal. The level adjustor receives a first signal having a level corresponding to a first control signal, adjusts the level of the first signal in response to a second control signal, and generates a level-adjusted first signal as a second signal. The parabolic amplitude adjustor receives the square signal and performs amplitude control such that the level of the second signal is equal to the amplitude of the square signal to generate an amplitude-controlled square signal. The parabolic signal synthesizer synthesizes the first signal and the amplitude-controlled square signal and generates a synthesized signal as a parabolic signal.
In one embodiment, the first control signal is an auxiliary contrast control signal for achieving white balance by adjusting the contrast of red, green and blue signals constituting the input video signal. In another embodiment, the first control signal is a contrast control signal for adjusting the contrast of the input video signal.